This invention relates generally to a braking control apparatus for a vehicle, such as an automobile, in which the braking action is based on a command resulting from the operation of a brake pedal, and more particularly, to a braking control apparatus which avoids the problem of slippage occurring due to the wheels locking, to thereby provide stable braking control.
The braking device provided for each wheel is operated by the pressure of the brake fluid. Brake fluid under pressure is supplied to each wheel cylinder from the master cylinder by the operation of the brake pedal. This brake fluid drives the brake piston provided in the wheel cylinder for applying a braking force against the rotary brake disc which is provided coaxial with the wheel of the automobile.
A piston, which is operated by the brake pedal to generate brake fluid pressure, is provided inside the master cylinder which is positioned near the driver's seat. Between the master cylinder and each wheel is located a brake pipe for the transmission of the brake fluid. An increase in the pressure results in the brake pipe expanding and changes in the compression of the fluid in the pipe, which in turn is the source of delays in pressure transmission.
When, upon operation of the brake pedal, the wheels begin to slip in relation to the ground and then lock, it is necessary that the braking force be immediately reduced to unlock the wheels and prevent slippage. What is desired is an antiskid control apparatus which detects the locking of the wheels and automatically controls the braking force. Various means have been considered for this kind of antiskid control apparatus.
For example, when wheel lock is detected, an electromagnetic valve, which is provided in the fluid passage between the master cylinder and the wheel cylinder, reduces the pressure of the fluid supplied to the wheel cylinder. In this case, however, any delay in transmission will result in a delay in response to the antilock operation, and any structure that improves the responsiveness is difficult to build.
Another example is a device which uses traction control such that the rotary force of the wheels is delivered efficiently to the ground. When slippage resulting from wheel spin is detected, the electromagnetic valve is operated to control the supply of fluid pressure to the wheel cylinder where slippage has occurred. In this case, as well, response cannot be controlled because of the transmission delay in the braking system.